cannabilism! help!

hey guys,
long time lurker. first post.
I've got a problem with 1 of my RIR's. She is pecking another bird at the base of her tail and has created quite a wound on the poor thing. What should I do? It seems to happen in the morning before I let them out of their coop. Am I making a mistake by not giving them access to their run at all times? I let them free range during the day but at night they go up in a chick n hutch. There's only 3 birds but maybe their cramped or hungry in the morning? I'm a city boy trying to learn some basic skills and could use any help you guys can offer. Should I quarantine her? If so, which one? The pecker or the peckee? thanks guys.

I would give them access to the run at all times so the lower hen can get away if she needs to. You may have to give her her own area for a while to let her heal because that other hen now has a taste for blood. Do you have a chicken tractor or can you make one and keep it in the coop?
As far as the wound, you can wash it and put neosporin on it. How does the wounded hen look? Is she sluggish or look sick? If not, treating the wound just like you would any other should do the trick.